Conventional internal combustion engines usually employ cam-operated valves driven from a camshaft, synchronization gears, chains, connecting rods and numerous other moving parts, including reciprocating pistons, all of which produce a substantial amount of vibration, wear and energy loss. In order to reduce or eliminate such undesirable factors, various types of rotary engines have been proposed, which use rotors having radial vanes cooperating with the inside surface of a cylindrical chamber or stator in which said rotors are eccentrically mounted. Typical examples of such previously proposed rotary engines are shown in U.S. Pat. No. 1,427,692 to T. C. Mahon et al, and U.S. Pat. No. 3,437,079 to D. Odawara. Such prior rotary engines suffer from deteriorating gas-tightness between the rotors and the walls of the stators due to rapid wear, inefficient cooling of the engine, lack of provision for effective air scavenging of the combustion space, unreliable fuel intake, noisy operation, excessive fuel consumption, large bulk and weight, and high cost of manufacture. Thus, there is a definite need for improvements with respect to these features, as well as for general simplification in construction.